If you are a fan of naval history, odds are you have seen the famous 25- or 26-inch thick section of turret face plate armor, meant for a Japanese Yamato class battleship, that was found at the Kure Naval Base in Japan after the end of WWII and brought back to the States for testing. Since 1947 it has been chilling at the Washington Naval Yard and is one of the most photographed artifacts there.
The damage is the result of a 16-inch/50 cal naval shell impacting it during ballistic testing at the Dahlgren Naval Proving Ground in October 1946.
The NHHC has a video all about it, and the full story is rather interesting.